Block copolymers (BCPs) are emerging as materials of interest for use in bottom-up nano-scale fabrication techniques. BCPs are composed of chemically distinct polymer chains (blocks) that are covalently bonded at their ends. The very small dimensions of features that can be inherently formed by block copolymers gives rise to possibilities difficult to achieve by more common lithographic processes.
Specifically, BCPs are copolymer systems in which a first block is a chain of NA repeating units of type A covalently linked to at least a second block that is a chain of NB repeating units of type B. A BCP of block A and block B is known as a diblock copolymer. In most cases the blocks are of polymers of sufficiently different structure that phase mixing does not occur and phase separation defines the morphology and properties of the block copolymer. The specific nature of the blocks, size of the blocks and number of blocks can be controlled to impose a desired morphology to the system. Characteristic diblock copolymer morphologies (i.e., known equilibrium mesophases) include spheres, cylinders, gyroid, and lamellae.
When a thin film coating of BCPs is annealed, the polymer self-assembles to form nano-scale structures due to microphase separation, often with dimensions in the range of 5 nm to 100 nm. In addition, this microphase separation of a block copolymer thin film can generate dense arrays of microdomains with periodicity as low as 10 nm. Such arrays have been used as lithographic masks to pattern various functional materials, and to create devices including nanocrystal flash memory, nanowire transistors, gas sensors and patterned magnetic recording media.
Block copolymer thin film self-assembly on an unpatterned substrate leads to close-packed arrays of features such as lines or dots, and, hence, have sparked interest for bottom-up nano-scale fabrication techniques, those which arrange smaller components into more complex assemblies, often by formation of the block copolymers on a substrate. However, these features generally lack long-range order, thus limiting their utility for fabrication of devices. Therefore to impose long-range order and generate microdomain geometries not observed in films formed on unpatterned substrates, substrate features, such as chemical or topographical patterns, may function as a template, or guide, block copolymer self-assembly in a top-down nano-scale fabrication technique where larger features are used to direct the assembly of smaller features.
An attractive approach to generate a template is electron-beam lithography (EBL) where it is possible to form template features that are patterned, small, and/or a specific desired geometry. However, the serial nature of EBL, and resulting cost in time and money, makes it advantageous to minimize the density of the EBL-written features required to template a given arrangement of block copolymer microdomains. Even in a production context in which EBL is used only to write a master pattern that is to be replicated by some higher-throughput mechanism (such as nanoimprinting), the time required just to write the master can be prohibitively long.
A challenge in template design is therefore to find a set of template features of minimum complexity that will deterministically program the block copolymer to form a desired final pattern, such as an interconnect level in an integrated circuit, which may contain both periodic and aperiodic features.
Templated self-assembly of block copolymer thin films can generate periodic arrays of microdomains within a sparse template, or complex patterns using 1:1 templates. However, arbitrary pattern generation directed by sparse templates has remained elusive.
Accordingly, there exists a need in the art for methods of templating complex pattern arrangements of self-assembled block copolymer films.